In previous studies, thyroid hormone was observed to determine which of two types of cardiac myosin differing in adenosinetriphosphatase activity and physiochemical characteristics was synthesized. Other hormonal and nutritional influences on the molecular characteristics of myosin and on muscle contractility will be examined. Human cardiac myosin will be characterized, and the influence of cardiac pathology and of hormonal and nutritional abnormalities will be studied. Studies will be continued on the serum growth factors that influence replication of vascular cells with the aim of purification of active factors and determination of their tissue specificity. Studies will also be carried out on the renin-angiotensin system.